This invention relates to oil base drilling fluids. More particularly, the invention relates to invert alcohol-in-oil drilling fluids having good rheological and fluid loss properties, while alleviating many of the problems associated with maintenance of the ionic strength of the internal water phase. They have good temperature stability and the emulsion is stable under a variety of conditions (weight, temperature, presence of drill solids, formation water, etc.)
Oil-in-water emulsion drilling fluids (or muds) generally comprise water, oil, emulsifier, clays or polymers, and various treating agents which control the physical, chemical and/or rheological properties of drilling fluids in wellbores. Oil-in-water emulsion type drilling fluids have been used advantageously in the oil well drilling industry for many years. Emulsion drilling fluids possess many advantages over regular muds such as increasing drilling rates, longer bit lives, improved hole conditions, and the like. The most commonly used emulsion drilling fluids are oil-in-water types wherein oil is the dispersed phase and water the continuous phase. Inverted or water-in-oil emulsions wherein oil is the continuous phase and water is the dispersed phase also have been used to advantage.
The selection of a drilling fluid is primarily dependent upon the geological formation being drilled and the problems associated with such formation. Principal concerns in selection of a drilling fluid are temperature of drilling conditions, formation of gas hydrates, shale dispersion, wellbore stability, and drilling fluid loss and environmental requirements. The present invention provides a drilling fluid additive which overcomes these and other problems in the art as more particularly disclosed hereinafter.